Micro-Electro-Mechanical System (MEMS) is a miniaturized system developed based on microelectronic technology. It is a micro integrated system that integrates physical, chemical and biological sensors (configured to perform information obtaining), actuators, and information processing and storage. Micro sensors, micro actuators, micro elements, micro mechanical optical electromechanical devices, vacuum microelectronic devices, and, power electronic devices manufactured by MEMS technology are widely used in aviation, aerospace, automobile, biomedicine, environmental monitoring, military affairs and almost all fields that men can expose.
Photolithograph is a processing step that appeared most often in the MEMS device manufacturing process, the quality and accuracy of photo lithograph directly affects the quality and accuracy of subsequent processes. Photolithograph can be divided into planar lithography and stereo lithography according to its spatial character.
MEMS photolithographic technology is developed based on integrated circuit (IC) technology. Firstly, photoresist (PR) is coated on a substrate, and a pattern on a mask is transferred on the substrate via exposure, developing and so on. The pattern of the photo resist can also be the mask for the subsequent process, being corroded and ion implanting, and finally the layer of photo resist is removed. After decades of researching on MEMS micro sensors and MEMS micro actuators manufactured based on silicon material and bulk silicon technology, relatively mature design method and process basic have existed, and begun to industrialize. Silicon material and bulk silicon technology is one of the important research areas of MEMS technology. The photo lithographic process of bulk silicon technology is different from that of IC technology.
In very large scale integration manufacturing process, deep trench isolation technology of silicon has become a necessary means to promote a higher level development of IC industry. Implementing the deep trench isolation technology in a complementary metal oxide semiconductor (CMOS) can effectively overcome the latch-up effect; while implemented in a bipolar circuit, it can greatly reduce the parasitic capacitance, and the increases breakdown voltage; and in a dynamic random access memory (DRAM) with more than four megabytes of storage space, the deep trench isolation technology is implemented to make the storage capacitor. All these applications depend on whether a deep trench can be obtained or not.
Deep reactive ion etching (DRIE) can obtain a high-aspect-ratio structure with a smooth surface, thus this micro fabrication technology becomes one of the mainstream technology in the fields of MEMS manufacturing.
During the corroding process of MEMS using DRIB, since the windows of the mask are different, the corrosion depths are also different. Referring to FIG. 1, using DRIE to corrode the silicon (Si), while the silicon dioxide (SiO2) is the mask, because the sizes of the two windows are different (A>B), generally, the corrosion depth of A is greater than the corrosion depth of B. If the depths are different, it will impair the performance of the product.
Accordingly, it is necessary to provide a silicon etching method, so that the etched silicon trenches have the same depth.